Stereotype mat



Patented Dec. 5, 1950 STEREOTYPE MAT Arlie William Schorger, Madison, Wis 9.88 8 to Burgess Cellulose Company, Freeport, 111., a

corporation 01 Delaware No Drawing. Application April 13, 1948, Serial No. 20,832

6 Claims. (01. 22--5.5

This invention relates to improvements in stereotype mats and particularly to that type of stereotype mat known in the art as a dry mat."

The stereotype mat of this type which is in common use consists of a relatively thick, moisture-absorbent sheet of felted cellulose fibers, such as rag stock, cotton linters and chemical wood pulp, such as alpha, sulphite or soda pulp. It usually contains a filler, such as powdered clay, talc, or the like mixed with the fibers, and the surface which is to receive the impression of the form containing the type, cuts, etc. may be given a coating to improve its smoothness and castability. Stereotype mats of such character and methods for making them are well known.

The mat is usually shipped and stored with a moisture content of to 25%, in which condition it is ready for use. The moisture renders it plastic so that it is capable of taking the impression of the form. After the impression has been taken, the mat is dried by being placed in a "scorcher, and in this condition it is placed in a casting machine and molten stereotype metal is poured against it to form a metal printing plate.

It is important that the mat in its moistened condition possess sufiicient plasticity to take a lull and exact impression of the form without the application of excessive pressure. fibers possess only a limited plasticity, which may be increased somewhat by fibrillation and hydration of the fibers by a beating operation prior to the formation of the mat. However, the improvement of plasticity by such method has limitations because hydration also causes increased shrinkage, hardness and buckling 0f the mat during the drying operation after it has been molded and before the printing plate is cast,

It is the object of the present invention to provide a stereotype mat having improved plasticity during molding such that it is capable of receivin a full, sharp and clear-cut impression from the mold with the application of relatively little pressure.

In accordance with the present invention, it has been discovered that an improved stereotype mat, free from the objections mentioned above and possessing greatly superior plasticity, is ob-' tained by having a water insoluble hydroxyalkyl P ether of cellulose present in the body of the mat. As an example, a stereotype mat composed of felted cellulose fibers which have been converted to a water insoluble hydroxyalkyl ether, which has been moistened so as to contain approximate- Cellulose g 1y 20% of water, takes an impression to the full depth of the type of the form upon the application of about one half of the pressure customarily used in molding. This is of great advantage in prolonging the life of the type and the cuts. The plasticity of the mat is improved to such an extent that after receiving the imprefiion the surface is so smooth as to have the appearance of a wax mold. While the reason for the greater plasticity is not fully understood, it is believed to be due to the presence of the hydroxyl radical of the hydroxyalkyl group, which has a high aflinity for water. It is believed that such radical causes the absorption oi a relatively great amount of water and that the water absorbed thereby is held in a manner which imparts a high degree of plasticity.

The cellulose hydroxyalkyl ether can be incorporated in the stereotype mat by an etherifying treatment of the cellulose fibers prior to the operation of felting the fibers into the mat. In such case, the fibers may be converted in whole or in part to the hydroxyalkyl ether. Another method of incorporating the cellulose hydroxy-' alkyl ether into the mat is by etherifying a quantity of cellulose fibers and mixing the etherified fibers with unetherified cellulose fibers and felting the mixture into a mat. Other methods will be described hereinafter. As a result of such methods the cellulose hydroxyalkyl ether is incorporated in and distributed throughout the body of the stereotype mat,

The fibrous structure of the stereotype mat is not altered, even though all of the cellulose may have been converted to cellulose hydroxyalkyl ether. Within a single fiber, the composition may be all cellulose, all cellulose hydroxyalkyl ether, or part celluose and part cellulose hydroxyalkyl ether. In any case, the fibers have a cellulose base and the cellulose hydroxyalkyl ether is distributed throughout the body of the mat.

The ethers which may be used are the hy-- droxyethyl and hydroxypropyl ethers of cellulose which are insoluble in water. Methods for making water insoluble cellulose hydroxyalkyl ethers are known, examples of which are described hereinafter and in United States Patent No. 1,863,208. In general, the process comprises reacting cellulose with an etherifying agent in the presence of a base, such as an alkali metal hydroxide or a tertiary amine. The base apparently does not enter into the reaction, except as a catalyst. As isknown, degradation of the cellulose by excessive aging thereof in the presence of the base prior to the etheriiying operation will produce a water soluble ether, and

\ to propyl inclusive. The etherification apparent-' 1y takes place by an addition reaction, and when employing ethylene oxide, it is believed that the reaction takes place as follows:

C|OI04.CH1OH CH:. H; v CsHlCHzOCHI-CH3OH Cellulose Etyhiyene Cellulose bydraxyethyl other The cellulose fibers which may be used in accordance with the present invention may be of any character which is ordinarily used in making stereotype mats, including rag stock, cotton linters, chemical wood pulp, such as alpha, sulphite or soda pulp, as well as fibers composed of filamentary regenerated cellulose such as rayon, and the like.

The concentration or proportion of cellulose 'hydroxyalkyl ether in the mat may vary over a relatively wide range. For example, when ethylene oxide'ls employed to etherify cellulose fibers before they are felted into a stereotype mat, marked benefits are obtained with an amount of ethylene oxide equal to from 6.5% to 41%, based on the dry weight of the fibers, and the preferred proportion is from 6.5% to 27.5% of ethylene oxide. In terms of the proportion of hydroxyalkyl radical to each cellulose unit in the stereotype mat, this amounts to 0.25 to 1.5 hydroxyalbl radicals to each unit of cellulose and the preferred range is 0.25 to 1 hydroxyalkyl radical for each unit of cellulose.

The term cellulose unit when used in the specification and claims, means the unit CsHmOs and is intended to include the cellulose molecule where the cellulose is not etherified, and the cellulose base of the hydroxyalkyl ether where the cellulose is etherified. While the extent to which the advantages of increased plasticity are obtained depends upon the number of hydroxyalkyl radicals which are present, any amount which may be present produces benefit and the invention contemplates broadly the incorporation of such radicals regardless of the proportions thereof, the aforesaid ranges being given to indicate the proportions at which the pronounced benefits are obtained. When using an etherifying agent other than ethylene oxide, a quantity is employed which will result in the presence of substantially the same proportion of hydrcxyalk radicals as is set forth heretofore.

Example 1 Into a shredder is placed a quantity of water containing a small amount of sodium hydroxide or a tertiary amine, such as pyridine. Coniferous alpha pulp is then added gradually to the shredder while the latter is in operation. The quantity of water is from 25% to 60%, and preferably from 40% to 50%, and the quantity of sodiumhydroxide is approximately 2%, or that of the tertiary amine is from 3% to 5%, based on the dry weight of the pulp. The operation is continued until the fibrous mass is shredded and the fibers thoroughly separated one from another. v

The mass is then transferred to a rotatable jacketed closed vessel which is continuously rotated and in which the mass is heated to a temperature of approximately 45 C. Ethylene oxide in an amount equal to approximately 13.6% of the dry weight of the cellulose fibers is gradually introduced while the rotation of the vessel is, continued until the etherification is completed. The sodium hydroxide or pyridine serves as a catalyst for the etherifying operation, in accordance with known practice. The time required for completion of the etherification depends upon the size of the batch and the rate of introduction of the ethylene oxide. The reaction is exothermic and the temperature is controlled by circulating water in the jacket of the vessel. I

The result of the operation is that the ethylene oxide converts the cellulose into cellulose hydroxyethyl ether. Substantially all of the ethylene oxide is consumed in the etherifying operation and the quantity of cellulose hydroxyethyl ether formed is such that there is one hydroxyethyl radical to every two cellulose units present in the fibrous mass.

The fibrous mass, without further treatment or heating is then felted into a stereotype mat by a paper machine in a manner well known in the art, which causes an inter-bonding of fibers. Although the mass contains a small amount of the sodium hydroxide or other catalyst, this is largely eliminated in the felting operation and a separate washing operation is not necessary. In accordance with common practice, the stereotype mat may have a thickness of from .020 inch to .040 inch. It is the stereotype mat so formed which is spoken of heretofore as taking a full and exact impression of the mold upon application of one half of the pressure customarily employed.

Example 2 A procedure similar to that of Example 1 is followed through the etherifying operation, and the resulting etherified cellulose fibers are beaten in a pulp beater for one hour, after which a powdered mineral filler such as clay or talc is added in an amount equal to 6% of the dry weight of the fibers. The resulting mass is thoroughly mixed and felted into a stereotype mat as described heretofore.

Example 3 A procedure similar to that of Example 2 is followed with the substitution of proylene oxide in an amount of 18%, based on the dry weight of the fibers, in place of ethylene oxide.

Example 4 A procedure similar to that of Example 1 is followed until the etherifying operation is completed. A quantity of the etherified fibers equal to 20% of the total is then dissolved in an aqueous sodium hydroxide solution containing 10% of sodium hydroxide, based on the weight of the solution. The solution containing the ether is then mixed thoroughly with the remaining of the etherified fibers, and to the mass isadded with agitation sufiicient of a dilute aqueous solution of mineral acid to neutralize the sodium hydroxide and precipitate the ether in intimate association with the etherified fibers. The mass is then felted into a stereotype mat in the same manner as described heretofore.

Example 5 A quantity of coniferous-alpha pulp is mercerized by soaking in an aqueous solution containing 30% of its weight of sodium hydroxide. The resulting mass is compressed to remove the excess sodium hydroxide solution and leave a residue the cellulose content of which is approximately 30%. This residue is subjected to a procedure similar to that of Example 1 with the exception that the etherifying agent is ethylene chlorohydrin instead of ethylene oxide, the amount of chlorohydrin being approximately 25% based on the dry weight of the cellulose fibers. The result is a. hydroxyethyl ether of cellulose which is present in an amount such that there is one hydroxyethyl radical to two cellulose units. To the mass is added sufiicient of a dilute aqueous solution of a mineral-acid to neutralize the sodium hydroxide present, and the fibers are then felted into a sterotype mat in the manner described heretofore.

Example 6 A mass of etherified cellulose fibers producedin accordance with the procedure of Example 1 is mixed with a mass of unetherified cellulose fibers in equal proportions by weight of etherified and unetherified fibers. The resulting mixture -is felted into a sterotype mat in accordance What is claimed is:

1. A stereotype mat of inter-bonded felted fibers and containing in the body thereof a water insoluble hydroxyalkyl ether of cellulose from ethyl to propyl inclusive, the'proportion of said ether being such that there are from 0.25 {01.5 hydroxyalkyl radicals to each unit of celulose.

2. A stereotype mat .of inter-bonded felted fibers of cellulose and a water insoluble cellulose hydroxyalkyl ether from ethyl to propyl inclusive, the proportion of said ether being such that there are from 0.25 to 1.5 hydroxyalkyl radi-' I cals to each unit of cellulose.

3. A stereotype mat of a mixture of interbonded felted cellulose fibers and fibrous water insoluble cellulose, hydroxyalkyl ether from ethyl to propyl inclusive, the proportion of said ether being such that there are from 0.25 to 1.5 hydroxyalkyl radicals to each unit of cellulose.

4. A stereotype mat of inter-bonded felted cellulose fibers, at least a portion of said fibers having been converted to a water insoluble hydroxyalkyl ether of cellulose from ethyl to propyl inclusive, the proportion of said ether being such that there are from 0.25 to 1.5 hydroxyalkyl radicals tb'each unit of cellulose.

5. A stereotype mat of inter-bonded felted fibers of a cellulose base and containing in the body thereof a water insoluble cellulose hydroxyalkyl ether from ethyl to propyl inclusive, the proportion of said ether being such that there are from 0.25 to 1.5 hydroxyalkyl radicals to each unit of cellulose.

6. A stereotype mat of inter-bonded felted fibers of a cellulose base and containing in the body thereof a water insoluble cellulose hydroxyalkyl ether from ethyl to propyl inclusive, the proportion of said ether being such that there are from 0.25 to 1 hydroxyalkyl radical to each unit of cellulose. ARLIE WILLIAM SCHORGER.

ENCES @I'EED The following references are of record an the file of this patent:

UNITED STATES PA Y:

Certificate of Correction Patent No. 2,533,145 December 5, 1950 ARLIE WILLIAM SCHORGER It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows:

Column 3, line 18, for C O O .CH OH read U H O L H OH; line 58, after the Word which strike out the; column 4, line 30, after of insert the; line 56, for proylene read propylene; line 68, for 80 read 80%; column 6, line 7, after cellulose strike out the comma; V and that the said Letters Patent should be read as corrected above, so that the same may conform to the record of the case in the Patent Oifice. Signed and sealed this 27th day of February, A. D. 1951.

[SEAL] THOMAS F. MURPHY,

Ass'is tant=00mmissi0ner of Patents. 

1. A STEREOTYPE MAT OF INTER-BONDED FELTED FIBERS AND CONTAINING IN THE BODY THEREOF A WATER INSOLUBLE HYDROXYALKYL ETHER OF CELLULOSE FROM ETHYL TO PROPYL INCLUSIVE, THE PROPORTION OF SAID ETHER BEING SUCH THAT THERE ARE FROM 0.25 TO 1.5 HYDROXYALKYL RADICALS TO EACH UNIT OF CELLULOSE. 